Electrochemical cells exist in which the electrodes are separated by an ion-exchange membrane, for example a solid polymer electrolyte (SPE). WO03/238980 teaches that ion-exchange materials can be produced based on hydrophilic polymers, i.e. polymers which are inherently able to absorb and transmit water through their molecular structure. Those hydrophilic polymer membranes are obtainable by the copolymerisation of a hydrophilic monomer (such as vinyl pyrrolidone), a hydrophobic monomer (such as methyl methacrylate), a monomer including a strongly ionic group (such as AMPSA) and water. It is important that the polymerisation is aqueous. This is necessary for good electrical and hydration properties.
The strongly ionic group can be cationic (forming a cationic exchange membrane) or anionic (forming an anionic exchange membrane).
Hydrophilic materials are particularly useful in hydrogen-oxygen fuel cells, since product water can be re-distributed, thereby avoiding local flooding or drying out of the membrane. In electrolysers hydrophilic membranes allow the easy transport of water to the surface and throughout the membrane. This allows water to be used on one side of the electrolyser only, reducing the balance of plant required in such systems. WO03/238980 teaches a methodology for forming ionically active sites by co-polymerisation from a solution of ionically active monomers.